Measurement uncertainty, reference change value, and total error of total and free prostate specific antigen tests
Abstract Objectives The dispersion of measurement results is defined as the measurement uncertainty (MU), and the reference change value (RCV) indicates whether the difference between the current result and previous results is significant. The purpose of this study is to evaluate whether the analytical performance of total PSA (tPSA) and free PSA (fPSA) measurements conforms to international quality standards by determining analytical coefficient of variation (CVA), Bias, MU, and RCV values and comparing them with European Federation of Clinical Chemistry and Laboratory Medicine (EFLM)’s allowable limits. Methods The study includes Internal Quality Control (IQC) and External Quality Assurance (EQA) results for the period from August 2021 to February 2022 of tPSA and fPSA. While the long-term CV was obtained from IQC for MU and RCV values, Total Error (TE) values were calculated with the monthly IQC CV and EQA bias. MU Extended values (MU%) are calculated according to ISO/TS 20914. Results The CVA of tPSA and fPSA was 3.44 % and 7.26 %, respectively. tPSA’s RCV and MU were found to be 17.78 and 9.74, and fPSA’s RCV and MU were found to be 23.7 and 15.23, respectively. Conclusions Our results indicate that tPSA demonstrates better analytical performance than fPSA due to its lower CV and bias values. We found that the RCV of a test, such as tPSA and fPSA, which play a key role in post-operative follow-up, must be calculated and shared with the surgeon. In addition, since the cut-off value decides whether or not to request a reflective fPSA, MU should also be calculated and reported.